The present invention relates in general to substrate manufacturing technologies and in particular to methods and apparatus for determining the endpoint of a cleaning or conditioning process in a plasma processing system.
In the processing of a substrate, e.g., a semiconductor wafer, MEMS device, or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate (chemical vapor deposition, plasma enhanced chemical vapor deposition, physical vapor deposition, etch, etc.) for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon.
In an exemplary plasma process, a substrate is coated with a thin film of hardened emulsion (such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing parts of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck. Appropriate etchant source gases (e.g., C4F8, C4F6, CHF3, CH2F3, CF4, CH3F, C2F4, N2, O2, Ar, Xe, He, H2, NH3, SF6, BCl3, Cl2, etc.) are then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate.
To ensure consistent plasma processing results, it is common practice to employ chamber conditioning processes prior to processing for every substrate. Chamber conditioning generally refers to a process that sets or resets the plasma chamber conditions to a substantially known state. For example, it is routine practice on dielectric etch plasma processing systems to remove residual hydrofluorocarbon polymers from the plasma chamber surfaces prior to processing the next substrate (i.e., without a substrate present), in a process known as waferless auto clean or WAC. WAC is commonly performed after a substrate has been processed, to ensure that the next substrate sees a standard, well-defined chamber condition, avoiding cumulative effects of pollutant byproduct buildup.
Generally comprised of organic and inorganic byproducts, pollutants are generated by the plasma process from materials in the etchant gases (e.g., carbon, fluorine, hydrogen, nitrogen, oxygen, argon, xenon, silicon, boron, chlorine, etc.), from materials in the substrate (e.g. photoresist, silicon, oxygen, nitrogen, aluminum, titanium, etc.), or from structural materials within the plasma processing chamber itself (e.g., aluminum, quartz, etc.).
Consistent plasma processing results may also be enhanced by be pre-coating the plasma chamber surfaces with a well-defined plasma-deposited film prior to processing each substrate to ensure a standard, well-defined chamber condition. Useful to avoid buildup of undesirable materials on chamber surfaces during the substrate processing, this method may reduce the time needed to recover from wet chamber cleans.
Conditioning the plasma chamber also may allow the surface chemistry of some plasma chamber materials to be more precisely controlled, such as the removal of oxidized surface films before processing each substrate. For example, Si tends to form a surface oxide when exposed to oxygen plasma. The presence of surface oxide as opposed to bare Si may have a significant influence on process results due to the well-known large variation in radical recombination rates on insulating as opposed to conductive surfaces. In addition, some plasma chamber conditioning processes may also require use of a dummy substrate that does not include microscopic structures, in order to protect the electrostatic chuck (chuck).
In these processes and others, it is important to determine when the endpoint of the process is reached. Endpoint generally refers to a set of values, or a range, in a plasma process (e.g., time) for which a process is considered complete. For conditioning, pre-coating, and surface chemistry control applications, the thickness of the material of interest is usually the most important value.
Referring now to FIG. 1, a simplified diagram of an inductively coupled plasma processing system is shown. Generally, an appropriate set of gases may be flowed from gas distribution system 122 into plasma chamber 102 having plasma chamber walls 117. These plasma processing gases may be subsequently ionized at or in a region near injector 109 to form a plasma 110 in order to process (e.g., etch or deposit) exposed areas of substrate 114, such as a semiconductor substrate or a glass pane, positioned with edge ring 115 on an electrostatic chuck 116.
A first RF generator 134 generates the plasma as well as controls the plasma density, while a second RF generator 138 generates bias RF, commonly used to control the DC bias and the ion bombardment energy. Further coupled to source RF generator 134 is matching network 136a, and to bias RF generator 138 is matching network 136b, that attempt to match the impedances of the RF power sources to that of plasma 110. Furthermore, vacuum system 113, including a valve 112 and a set of pumps 111, is commonly used to evacuate the ambient atmosphere from plasma chamber 102 in order to achieve the required pressure to sustain plasma 110 and/or to remove process byproducts.
Referring now to FIG. 2, a simplified diagram of a capacitively coupled plasma processing system is shown. Generally, capacitively coupled plasma processing systems may be configured with a single or with multiple separate RF power sources. Source RF, generated by source RF generator 234, is commonly used to generate the plasma as well as control the plasma density via capacitively coupling. Bias RF, generated by bias RF generator 238, is commonly used to control the DC bias and the ion bombardment energy. Further coupled to source RF generator 234 and bias RF generator 238 is matching network 236, which attempts to match the impedance of the RF power sources to that of plasma 220. Other forms of capacitive reactors have the RF power sources and match networks connected to the top electrode 204. In addition there are multi-anode systems such as a triode that also follow similar RF and electrode arrangements.
Generally, an appropriate set of gases is flowed through an inlet in a top electrode 204 from gas distribution system 222 into plasma chamber 202 having plasma chamber walls 217. These plasma processing gases may be subsequently ionized to form a plasma 220, in order to process (e.g., etch or deposit) exposed areas of substrate 214, such as a semiconductor substrate or a glass pane, positioned with edge ring 215 on an electrostatic chuck 216, which also serves as an electrode. Furthermore, vacuum system 213, including a valve 212 and a set of pumps 211, is commonly used to evacuate the ambient atmosphere from plasma chamber 202 in order to achieve the required pressure to sustain plasma 220.
In view of the foregoing, there are desired methods and apparatus for determining the endpoint of a cleaning or conditioning process in a plasma processing system.